SHAPIRO: Well, many of you wrote in to say, hey, I know my bivalves. That's no clam.

CORNISH: So what is it? Well, the Uffizi Gallery in Florence where the painting usually hangs expertly dodges the question. Its guide to the artwork says Venus is portrayed naked on a shell on the seashore. On her left, the winds blow gently, caressing her hair with a shower of roses.

SHAPIRO: OK, no help there, so we called an expert.

ELLEN STRONG: I know this painting very well, yes, of course. It's a classic. My name is Ellen Strong, and I study snails, which is not really a great way to introduce yourself at a cocktail party.

SHAPIRO: OK. Strong is being modest. She doesn't just study snails. She is a mollusk expert at the National Museum of Natural History here in Washington, D.C. We pulled up an image of the "Birth Of Venus" on the computer and told her to go take a look. Name that shell.

STRONG: So the scientific word would be pecten. Considering that Boticelli lived in Italy, this may have been a species called Pecten jacobaeus.

SHAPIRO: Pecten jacobaeus, of course.

CORNISH: In layman's terms...

STRONG: It is definitively a scallop shell. No question.

SHAPIRO: Not a clam.

STRONG: The most prominent feature are those radiating features of the shell. That is very characteristic of a scallop shell.

CORNISH: OK, but Botticelli was painting hundreds of years ago - the 15th century, in fact. Is it possible that shells have changed since then?

STRONG: No (laughter).

CORNISH: All right, all right, fine. Definitely a scallop, right?

ANTHONY COLANTUONO: Well, it's not a clam shell (laughter) but does it really matter in this day and age of ours what kind of shell it is?

SHAPIRO: That's Anthony Colantuono, specialist in Renaissance and Baroque art history at the University of Maryland, College Park.

COLANTUONO: Even I, who am the most persnickety of art historical iconographers, wouldn't think of that as an offense to all, you know, kind of crustaceans and gastropods.

CORNISH: Colantuono says what may have added to our cockle confusion is that even in the art world, the "Birth Of Venus" lends itself to a certain shorthand.

COLANTUONO: A lot of our historians have called it "Venus On The half Shell" from the podium in the lecture hall. You know, it's just a colloquial thing. So I find it, you know, somewhat amusing. Of course, being the persnickety iconographer I am, if I was writing a formal art historical article, I would find out what kind of a shell it was and, you know, put that in there.